This invention relates to uncured rubber compositions which are modified to improve the properties of vulcanized rubbers prepared therefrom, and to the vulcanized rubbers themselves. The invention also relates to methods of improving the properties of cured rubber compositions such as increased rebound, reduced hysteresis and reduced rolling resistance when the modified rubber compositions are utilized in tires. More particularly, the present invention relates to uncured rubber compositions which are modified by the attachment therein of aromatic six-membered heterocyclic nitrogen-containing groups such as may be derived from pyridine compounds.
It is known that rubber compositions generally are combined or "compounded" with various other materials before being cured and/or put into use. Some of these added materials improve the properties of the end product in service while others improve processing properties of the uncured compositions. In some instances, both effects may be achieved. It is also known that the various chemicals, pigments and other materials so used, both organic and inorganic, can interact in various ways to produce desirable or deleterious effects. For further discussions of rubber processing and materials used therein, see, for example, Encyclopedia of Polymer Science and Technology,, published by John Wiley and Sons, N.Y. (1970), particularly Vol. 12, page 280 and The Vanderbilt Rubber Handbook, R. T. Vanderbilt Company, Norwalk, Conn., 06855 (1968), particularly Sections 6, 7, 8, 9 and 11.
Vulcanizing agents, anti-degradants, plasticizers, extenders, fillers, pigments, etc. generally are incorporated into vulcanizable rubber compositions so that the rubber can be cured or vulcanized in a mold to form useful articles. It often is necessary to include processing aids in rubber compounds prior to molding and curing. These processing aids are primarily intended to improve the mixing of the ingredients of the rubber compound, the processability of the rubber, the mold or mill release properties of the rubber, tack and green strength without seriously adversely affecting the properties of the cured rubber.
Carbon blacks are used in rubber formulations and vary widely as to their characteristics, and effects on rubber formulations. In rubber formulations, carbon black is used as a reinforcing filler. Many carbon blacks of the channel and furnace types with varying characteristics have been utilized because they impart varying desirable characteristics to the rubber.
In recent years, the desirability of reducing the rolling resistance of a tire and the improvement of its braking properties on a wet road surface, i.e., wet skid resistance, have been motivating forces for considerable research, particularly since the two properties are inherently incompatible. Many methods suggested for modifying polymers to improve the wet skid resistance of tire surfaces have resulted in an increase in rolling resistance, and conversely, many suggestions made for reducing rolling resistance generally have resulted in a reduction of the breaking properties of the tires on wet road surfaces.
It is generally accepted that in order to reduce the rolling resistance of tires, the tread rubber material should have a high rebound. It is known that rebound and rolling resistance are in inversely related to each other, and therefore, the higher the rebound of the cured rubber, the lower its rolling resistance.
Many suggestions have been made in the prior art for modifying unsaturated rubbers to improve a vulcanized form of the rubber with respect to low rolling resistance and high wet skid resistance. One technique which has been suggested involves the reaction of active polymer molecules having an alkali metal or an alkaline earth metal at their ends by reacting the ends with various compounds such as specified aromatic thioketone compounds which introduce an SH group into the ends of the polymer (U.S. Pat. No. 3,755,269). More recently, two British published applications describe methods for modifying unsaturated polymer rubbers by reacting an alkali metal-containing unsaturated polymer end groups with an aromatic ketone such as Michler's ketone (4,4'-bis(dimethylamino)benzophenone). Such modified unsaturated elastomers are reported to be useful in tire compositions for improving the wet skid resistance and rebound characteristics (GB 2,117,778A and GB 2,121,055).